1.Field of the Invention
This invention relates to a flame-retardant resin composition and, more specifically, it relates to a flame-retardant resin composition, comprising a thermoplastic polyester which displays a excellent mechanical property and thermal stability.
Flame-retardant resin compositions comprising thermoplastic polyesters using organic halide compounds as the main ingredient have suffered from a problem in their thermal stability. Particularly, flame-retardant resin compositions composed of polyethylene terephthalate are excellent in their heat-resistance but have a relatively high molding temperature and exhibit remarkable heat degradation upon molding. A flame retardant resin composition comprising thermoplastic polyester having an improved thermal stability is disclosed, for example, in Japanese Patent Application (OPI) No. 195142/82 (the term "OPI" herein used means "unexamined published application"). In this composition, the surface of antimony trioxide added for providing flame-retarding property is treated with an alkoxysilane to form membrane inactive to the hydrolysis of the thermoplastic polyester thereby improving the thermostability. However, as can be seen from the examples of Japanese Patent Application (OPI) No. 195142/82, the mechanical strength, particularly the tensile strength of the molding product is relatively low and not yet sufficiently satisfactory for specific uses. Japanese Patent Application No. 2357/82 describes that covered antimony oxide has no thermal stability of commercial value. Japanese Patent Application (OPI) No. 2357/82 describes a specific composition which is excellent in the thermal stability. According to the specification thereof, when a particular substance for improving the crystallizing rate and an antimonate salt of a metal belonging to group I, II and VIII of the Periodic Table, are used together in a flame-retardant, they do not have adverse effects on the thermal stability and improve the flame-retardancy. Generally, since crystallization stimulators tend to reduce the mechanical strength of the resin composition, their use is limited. Further, the possible range of applying this technique is limited since the effect can only be obtained in the combined use of a specific crystallization stimulator and an antimonate salt. Accordingly, a flame-retardant resin composition composed of a thermoplastic polyester having a relatively high mechanical strength and, at the same time, excellent thermal stability has been demanded.